1. Field of the Invention:
This invention relates to a method for recording a picture such as a wiring pattern or the like by printing the picture on a picture-forming material coated with a film of a photosensitive material, such as a board suitable for use in the fabrication of a printed circuit, in accordance with input picture signals without development of dimensional distortion.
2. Description of the Prior Art:
It is proposed in U.S. Pat. Ser. No. 582,085 filed Feb. 21, 1984 claiming Convention Priority on Japanese Patent Application No. 47890/1983 of Mar. 24, 1983 and concurrently with the present case and commonly assigned to the same assignee to store two-dimensional picture data corresponding to a desired picture or pattern as digital picture signals in a memory or the like and then to form the desired picture or pattern on a picture recording material without dimensional distortion by means of a sweeping light beam controlled by the picture signals.
In the above-proposed method, a light beam having such a light quantity that does not substantially expose the picture recording material is allowed to reach the picture recording material whenever a picture-free portion of the picture recording material is scanned. A portion of the picture-recording and sweeping light beam per se is branched out, whereby to detect a position corresponding exactly to a swept point on the picture recording material. On the basis of a resulting position signal, there is produced a feedback signal which is adapted to control the timing of the optical modulation.
In the above method, a portion of a recording light beam is branched out by a half-mirror or the like and two different levels are given to the recording light beam so as to obtain position signals corresponding to sweeping light beams. Since a photosensor having a single level of sensitivity is used for sweeping light beams both when only a small light quantity that does not substantially expose the picture recording material is allowed to reach the picture recording material and when a picture portion is recorded on the picture recording material, the level of the sweeping light beam having a small light quantity and adapted to scan a picture-free potion may become unduly different from the level of the sweeping light beam having a large light quantity and adpated to scan a picture-bearing portion. The levels of resulting pulse signals may thus be varied, thereby instabilizing the processing of the light beam delivered from the light beam source which processing is supposed to be synchronized with the picture signals.